1. Field of the Invention
The present invention relates to a method and system for establishing a call on a communication network. More particularly, the present invention relates to an improved method and system for transmitting dialed digits from a remote station to a base station in a fixed wireless system.
2. Discussion of the Related Art
In conventional telephone networks, telephones (or more broadly, the communication terminals) are connected to local switching facilities by local telephone lines, and the switching facilities are interconnected via trunk lines. Depending upon the geographic distribution of the population the telephone network is to serve, the cost of installing local telephone lines may be prohibitive. For this reason, some of the more sparsely populated areas in the world do not have access to a public communication network.
In an effort to bring modern communication to these sparsely populated areas, a system known as a fixed wireless system has been developed. In general, a fixed wireless system replaces the local telephone lines with a wireless radio link that operates in a manner similar to cellular networks. These fixed wireless systems typically do not require specialized communication terminals, but permit standard telephones, fax machines, and computers modems to be used.
An example of a fixed wireless system is shown in FIG. 1. The fixed wireless system includes remote stations 10 to which telephones 15 are wire connected, base stations 20 and 25, and at least one mobile switching center 30, which provides a gateway to a communication network 40.
In general, remote stations 10 include a cellular transmit/receive module and an interface, which permits a standard telephone 15 and a standard cellular transmit/receive module to interact.
Base stations 20 typically include transmit/receive modules, a processor, and an interface for connecting base stations 20 with mobile switching center 30. Base stations 20 communicate with mobile telephones 16 and portable telephones 17, as well as remote stations 20, via radio links. Base stations may also take the form of base station 25 in which a base station controller 26 controls one or more base transceiver stations 28.
An example of a fixed wireless system is described in U.S. Pat. Nos. 4,922,517 and 4,775,997 issued to West, Jr. et al. In the system disclosed in these patents, a processor is provided in the remote stations to simulate a conventional telephone network. More specifically, the processor provides a simulated dial tone to the telephone when the telephone is taken off-hook, performs a digit analysis to determine when the last digit has been dialed, and transmits all the dialed digits to a base station upon determining that dialing is complete. Thus, unlike conventional cellular systems, the user is provided with a dial tone and does not have to press a "SEND" key after entering all the digits to originate the call request.
One problem associated with having a processor in the remote station provide a simulated dial tone to the telephone in response to the telephone being taken off-hook is that the simulated dial tone may not accurately reflect whether a connection can be made with the communication network, whereas a real dial tone indicates that a connection with the communication network has actually been established. If, for example, the only base station in range is congested with traffic and is not accepting additional calls, the processor in a remote station will inaccurately provide a simulated dial tone to the connected telephone, giving the user the false impression that the call will go through.
Another problem with the above described system arises from the various calling protocols and dialing plans existing in different countries (i.e., the number of digits required to make a call). In order to accommodate the calling protocols of a particular country, digit analysis performed by the processors in the remote stations must be modified. Moreover, if the calling protocol in a country is modified after the fixed wireless system is installed, every remote station must be altered to accommodate the modification. Because these remote stations are numerous and variously located at numerous homes and offices, the cost of installation or subsequent modification becomes excessive.